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In the alley-center infiltration approach, permeable material (asphalt, concrete, or pavers) is placed in the center of the alley and high-albedo concrete is placed along the outer edges. This way, water soaks through the center of the alley, but truck tires roll on top of the stronger pavement.
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    Each of Chicago's four pervious-pavement designs can be tweaked to fit just about any alley in the city. This is an example of full-alley infiltration using permeable pavement. Source: Chicago DOT

“My big fear is that people will see this project as just being about resolving standing water issues,” confirms Cindy Williams, CDOT quality assurance manager. “That's not our goal.”

The green alley project also falls in line with Chicago's initiative to build an environmentally sustainable city, providing CDOT with an opportunity to develop and test low-impact and recycled materials for infrastructure. This will help set a standard for other projects in the city, and nationwide.

Other green alley features that have nothing to do with stormwater include:

  • “Dark sky”-compliant light fixtures that direct light downward, where it is needed, and not up into second-story windows. The energy-efficient street lights' metal halide lamps provide white light that reduces glare and helps people distinguish color at night. The lights reduce light pollution so residents can see the stars.
  • High-albedo concrete, which is light in color and reflects sunlight away from the surface to reduce the amount of thermal energy released from pavement (i.e. the urban heat island effect). The concrete is made with granulated recycled slag, which is a byproduct of smelting ore to produce or purify metals.
  • The city also encourages residents to install rain roofs and plant shade trees.

    “If we can make our communities cooler, we're keeping them healthier at the same time,” says Leopold.

    The how-to handbook

    To ensure its newly constructed “green alleys'' will be properly maintained, Chicago DOT held pre-construction meetings with residents. The department also published a handbook that includes tips for making residential property environmentally sustainable. Download the handbook at www.cityofchicago.org/cdot (click on “green alleys”).

    Read other articles in our "Green Matters" special report:

    • Team Green: introduces you to a water district that decided to build green, and offers tips on how you can do it, too. It also provides a snapshot of how the solid waste department serving Florida's capital implemented a green demolition of its administration building.
    • Auditors Welcome: shows how auditing a department's facilities can provide a step-by-step plan for using less electricity and water.
    • Low-Impact Leader: our Q&A with Seattle's low-impact development program manager will give you ideas on how to incorporate their trail-blazing solutions into your own plans.
    • Resource List: A list of useful links for organizations and associations that can help you make you're department more sustainable, and planet-friendly.